1. Field of the Invention
This invention relates to a new and impoved apparatus for measuring the rate of movement of one object with respect to another. More particularly, this invention relates to a new and improved apparatus for measuring and recording the rate of penetration of a drill bit as it proceeds downwardly during oil well drilling operations.
2. Description of the Prior Art
During the operation of many industrial systems it is often beneficial, if not essential, to measure the rate of movement of one object with respect to another. For example, in the oil and gas well drilling industry, it is desirable to continually monitor and record the rate of penetration of the rotary drill bit as it proceeds through the various formations of the earth. This rate is often used as a tool to determine the drilling efficiency under variable operating conditions and the nature and characteristics of the individual formations which assist in the evaluation of potential hydrocarbon bearing zones.
Many times it is possible to measure the progress of a drill bit or other device if one can obtain accurate and meaningful measurements of the movements of any lines attached directly or indirectly to the drill bit or other device. This is particularly so with regard to a rotary drilling rig. Since the rotary drive member or kelly of a rotary drilling rig is attached directly to the upper portion of the drill string, its vertical movement with respect to the derrick floor is equal to the movement or penetration of the drill bit. Thus, a number of devices have been used to measure the movement of a cable attached at one end to the conventional tackle mechanism of the rotary drill rig in order to determine the progress of the drill bit. Such devices generally use measuring wheels to impart the movement of the cable to a drive shaft, which in turn imparts its motion to a pen arm through a complex series of levers, members and gears.
One such device is disclosed by Suter in U.S. Pat. No. 3,076,966, which employs a planet-sun gear mechanism to impart the motion of a drive shaft to an angular pen arm and provides an apparatus for disconnecting the pen arm from the measuring wheels and indicating this condition on a chart. However, Suter fails to provide for an adjustment of scale while drilling occurs. Additionally, the rate of progress of the drill bit or other device is not readily obtained from the chart, since only a series of independent marks is produced and manual calculations are requred to determine the rate either at any particular instant or over a period of time. Such manual calculations have been found to be not only inefficient, but also conducive to error.
Melton, U.S. Pat. Nos. 2,980,486 and 3,010,777, employs an integrally mounted five-point star actuating member and a cam in conjunction with a collar placed upon a drive shaft with arms extending from the collar to impart the motion of the drive shaft to a pen arm shoe and hence to the pen arm. Although Melton U.S. Pat. No. 3,010,777 provides for an adjustment to scale during drilling, this is only accomplished through an additional series of shafts, gears and arms. Additionally, devices described in both of these patents produce a series of marks in a manner analogous to other prior art devices, such that the rate of penetration of the drill bit is not readily obtained.
The foregoing, as well as other prior art devices, also suffer from other defects. For example, the pen arm is not designed to produce a particularly flat set of chart grid lines so as to facilitate comparison of other variables being recorded on a drum chart. Additionally, in order to disconnect the recording mechanism, prior art devices rely on purely mechanical links, which are necessarily located on the recording apparatus.